1. Field of the Invention
The present invention relates to an oil filter for the cleaning of lubricating oil, in particular for internal combustion engines of motor vehicles, having a filter housing with a connectable, screw-on cap. The housing is arranged at least approximately upright in the installed condition. There is a ring-shaped filter insert detachably connectable with the cap, whereby provision is made in the filter housing for an oil inlet for contaminated oil leading to the inflow space surrounding the filter insert, and for an oil outlet for cleaned oil from the flow-off space formed by the interior space of the filter insert. Furthermore, provision is made in the lower zone of the filter housing for a discharge duct connected with an oil-collecting space for oil that remained in the filter housing when the filter insert is changed. This discharge duct is automatically opened by a valve-like acting member with each change of the filter insert, but is otherwise constantly closed off.
2. The Prior Art
A known type of oil filter is described in EP-PS 03 14 915. A valve-like member is centrally arranged in the valve housing. There, it is subjected to the action of pressure springs acting in opposite directions relative to each other, of which the spring acting upon the valve-like member in the closing direction is supported on the filter insert. When the filter insert is removed, the force of the pressure spring acting in the closing direction disappears, so that the other pressure spring acting oppositely in the opening direction is capable of actuating the valve-like member in the opening direction, and thus is capable of releasing the opening to the discharge duct. Since in this connection the one pressure spring engages the filter insert unsymmetrically, the latter is stressed unsymmetrically in a disadvantageous way. Moreover, with this prior art design, the filter insert can be detached from the cap only in a troublesome way.